Method for the production of piston-type accumulators

ABSTRACT

The invention relates to a method for producing piston-type accumulators comprising an accumulator housing ( 10 ) and a separating piston which can be displaced in a longitudinal direction inside the accumulator housing ( 10 ) and separates two working spaces located therein. The end faces of the accumulator housing are sealed by means of one respective cover part ( 20 ). Previously known production methods are further improved due to the fact that the cover part ( 20 ) is fixed on one side ( 40 ) thereof via the free longitudinal edge ( 32 ) of the accumulator housing ( 10 ), which is displaced towards the cover part ( 20 ) in order to do so, such that a functionally and positionally secure connection of a cover part is ensured within the housing of a piston-type accumulator without using standard threaded connections.

The invention relates to a method for the production of piston-typeaccumulators having an accumulator housing and a separating piston,which is displaceable in the longitudinal direction in the accumulatorhousing, separating two working chambers from each other and whichaccumulator housing is sealed on each of the end sides by a covercomponent.

Piston-type accumulators are, in the broadest sense of the term,so-called hydraulic accumulators, which among other things serve thepurpose of admitting specific volumes of a pressurized liquid (hydraulicmedium) of a hydraulic system and returning these volumes to the systemwhen required. Since the hydraulic medium is pressurized, hydraulicaccumulators are treated as pressure reservoirs and must be designed forthe maximum excess operating pressure, the acceptance standards ofvarious installing countries being taken into consideration.Hydropneumatic (gas-charged) accumulators with a separating element arecurrently used in most hydraulic systems, a piston which separates afluid space as working chamber from a gas space as additional workingchamber serving as separating element inside the accumulator housing ofthe piston-type accumulator. Nitrogen is generally used as the operatinggas and the gas-tight piston to a great extent permits disconnection ofthe gas space from the fluid space.

The fluid component is connected to the hydraulic circuit so that, asthe pressure rises, the piston-type accumulator admits fluid and the gasis compressed in the process. As the pressure drops the compressed gasexpands and displaces the pressurized fluid back into the hydrauliccircuit. One advantage of piston-type accumulators is they can Awork@when in any position, but preference is to be given to verticalpositioning with the gas side on top, so that settling of foulingparticles from the fluid on the piston seals is prevented.

Consequently, the essential components of a piston-type accumulator arean outer cylindrical tube as accumulator housing, the piston asseparating element with its sealing system, and the sealing covers onthe end, which as cover elements simultaneously also contain a fluid anda gas connection. Two functions are regularly assigned to theaccumulator housing, specifically storage of internal pressure andensuring control of the piston inside the accumulator housing. The covercomponents on the front surface sealing the interior of the accumulatorhousing off from the exterior are provided on the outer circumferencewith external threading which may be screwed into a corresponding innerthreading along the free longitudinal edge over an assigned path.Production of the respective threaded connection is time-consuming; thisfactor correspondingly increases the production costs of the piston-typeaccumulator. In addition, safety measures must be taken in order tosecure in its position the cover component introduced.

On the basis of this prior art as disclosed, the invention has theobject of improving the disclosed manufacturing process for piston-typeaccumulators to the end that a reliable operation of a cover componentsecured in position in the accumulator housing is guaranteed while theotherwise customary threaded connections are avoided. This object isattained by a method having the characteristics specified in claim 1 inits entirety.

In that, as specified in the characterizing part of claim 1, the covercomponent on one of its sides is fastened by the free longitudinal edgeof the accumulator housing, which edge is for this purpose moved ontothe cover component, and, the otherwise customary screw connection beingavoided in the case of the respective cover component, a sort ofclamping onto the free end of the accumulator housing is achieved inwhich the cover component is clamped at least over the free longitudinaledge of the accumulator housing after this housing has been moved ontothe cover component, it being sufficient if a part of the freelongitudinal edge effects the clamping in question.

In one preferred embodiment of the method claimed for the inventionprovision is made such that at least one of the two cover components isinserted by one side opposite the other side to come up against a stopin the interior of the accumulator housing and/or such that therespective cover component is retained in its end position by theclamping force of the longitudinal edge introduced. If a stop isprovided on the inside of the accumulator housing, the cover componentmay be immobilized against this stop during the positioning movement ofthe free longitudinal edge of the accumulator housing. In addition or asan alternative, however, the possibility exists of inserting the covercomponent into the free end of the accumulator housing and theninitiating the positioning movement of the free end of the accumulatorhousing. The positioning movement may be effected toward the upper sideof the cover if the cover component is retained in a suitable position,but it is also conceivable that an unrestrained positioning movement maybe effected for the longitudinal edge and then, in the state ofreadiness for operation, the cover component may be moved by the pistonagainst the free longitudinal edge, which then effects the clampingthere.

By preference provision is also made such that a shaping tool isprovided for the positioning movement of the longitudinal edge of theaccumulator housing, a tool which is provided with positioning bevelsand positions the longitudinal edge of the accumulator housing on thecover component in such a way that this cover component is secured inthe accumulator housing as the clamping seat referred to.

In one especially preferred embodiment of the method claimed for theinvention two shaping tools positioned on opposite sides carry out thefastening process for the respective end cover component in a commonpositioning movement to the accumulator housing, these shaping toolsacting on the free longitudinal edge of the accumulator housing. It hasbeen found to be highly advantageous for the purpose of generation ofhigh fastening forces to position the two free ends of the cylindricalaccumulator housing uniformly, the shaping tool which acts on one end ofthe accumulator housing being capable in addition of reliablywithstanding the forces which are introduced into the accumulatorhousing by the other shaping tool.

Other advantageous embodiments are specified in the other dependentclaims.

The method claimed for the invention will be described in detail belowwith reference to the drawing, in which, in the form of diagrams notdrawn to scale,

FIG. 1 presents a longitudinal section of a piston-type accumulatorpresent in the state of the art;

FIG. 2, presents a longitudinal section of the upper part of the firstembodiment of a piston-type accumulator with a shaping tool positionedabove it;

FIGS. 3 and 4 present a longitudinal section of the positioning of apositioning tool on the free end of the accumulator housing for thepurpose of fastening the respective cover component;

FIGS. 5 and 6 a longitudinal section of the upper areas of theaccumulator housing in the form of two different versions with insertionbevels positioned in the interior for introduction of the respectivecover component;

FIG. 7 also presents a longitudinal section of the upper part of asecond embodiment of a piston-type accumulator housing with modifiedcover component.

The piston-type accumulator of the prior the art shown in FIG. 1 has asaccumulator housing 10 an outer cylindrical tube into which a piston 12with its sealing system 14 on the exterior has been introduced asseparating element so as to be longitudinally displaceable. Inside theaccumulator housing 10 the piston 12 separates two working chambers 16,18 from each other, one working chamber 16 serving to receive anoperating gas, in particular one in the form of nitrogen, while theother working chamber 18 forms the so-called fluid space for thepiston-type accumulator. The displaced position of the piston 12 andaccordingly the volume percentages of gas and fluid in the workingchambers 16 and 18 vary with the operating situation of the accumulator.There is mounted on the end of the accumulator housing 10 a covercomponent 20, 22 having a gas connection 24 for recharging with nitrogenoperating gas and a fluid connection 26 for connecting the piston-typeaccumulator to an overall hydraulic system not shown in detail.

Each of the two cover components 20, 22 is provided with externalthreading 28 which may be engaged with internal threading 30 which ismounted so as to extend along the free longitudinal edge 32 and outwardto the exterior. On the external circumference side the respective covercomponent 20, 22 is provided with a seal 34 for sealing the interior ofthe accumulator housing 10 from the exterior. Application of the lengthsof threading 28, 30 entails a certain production effort which makes theprior piston-type accumulators complex and expensive to produce. It isalso necessary to secure each cover component 20, 22 from rotation inorder to ensure its fixing in position inside the accumulator housing10. One possible method of securing the respective cover component 20,22 from rotation may be represented by providing a conventional adhesiveseal along the threading 28, 30 or by keeping the cover component in itsposition by means of a conventional retention bore (with and withoutthreading).

On the basis of this solution of the prior art the method claimed forthe invention will now be described in greater detail with reference toFIGS. 2 and the following. This solution permits cost-effective creationof a reliably operating connection of cover component and the associatedaccumulator housing 20. For the sake of greater simplicity ofpresentation, only the upper end of the accumulator housing 10 is shownin FIG. 2, along with the upper cover component 20. When reference ismade to these structural components below, as with the prior artembodiment shown in FIG. 1 the respective structural components aredesignated by the same reference numbers as in FIG. 1.

The method claimed for the invention is among other things characterizedin that the respective cover component, in this instance cover component20, is inserted by its lower side to come into contact with a stop 38 inthe form of an annular surface in the interior of the accumulatorhousing 10, the component being secured on its opposite side 40 by thefree longitudinal edge 32 of the accumulator housing 10, thelongitudinal edge 32 undergoing a positioning movement to the covercomponent 20, as is to be explained in greater detail in what follows.

A shaping tool 42 serves to position the longitudinal edge 32 of theaccumulator housing 20, this shaping tool 42 being provided with atleast one positioning bevel 44 which positions the longitudinal edge 32on the cover component 10 so that this component is secured as aclamping seat in the accumulator housing 10 between the stop 38 and thelongitudinal edge 32. For the purpose of establishing the respectiveclamping seat the upper side 40 of the cover component 20 is providedwith a contact surface 46 which is mounted so as to taper toward thelongitudinal axis 48 of the accumulator housing 10. The inclination ofthe respective contact surface 46 corresponds to the inclination of thepositioning bevel 44 of the shaping tool 42. However, other obviousinclinations or bevels are also conceivable. As is shown in FIG. 2, thepositioning direction for the shaping tool 42 is that of thelongitudinal axis 48 of the accumulator housing 10 or of the piston-typeaccumulator as a whole.

For the sake of greater clarity of illustration the separating elementin the form of the piston 12 has been omitted from FIG. 2, as has alsothe gas connection 24 shown in FIG. 1, which is also an integral part ofthe upper cover component 20. Before the clamp connection has beeneffected by way of the shaping tool 42, the upper free end of theaccumulator housing with its upper longitudinal edge 32 has an outlineas shown in FIGS. 3 to 6. The wall thickness of the longitudinal edge 32has been reduced in comparison to the rest of the accumulator housing10, the area of transition between the different wall thicknessesforming the stop 38 for the cover component 20. In addition, thelongitudinal edge 32 is provided with a tapering insertion bevel 50, bypreference on its side facing the cover component 20, the bevel beingoriented outward. The respective insertion bevel 50 facilitatesintroduction of the cover component 20 into the free upper end of theaccumulator housing 10, as will be described in greater detail below.

As is shown in FIGS. 4 and 5 in particular, the free longitudinal edge32 may also be provided on the external circumference side with a slidebevel 52 oriented toward the free end of the accumulator housing 10.This makes it easier for the longitudinal edge 32 to effect transitionfrom its cylindrical shape as shown in FIGS. 3 to 6 to an inclinedposition after being positioned, the slide bevel 52 then sliding alongthe positioning bevel 44 of the shaping tool 42 until the latter isvisibly mounted on the accumulator housing 10 in the direction ofpositioning. Once the positioning movement by the shaping tool 42 hasbeen completed, the longitudinal edge 32 is inclined along its contactsurface 46 onto the cover component 20 to form a fastening bevel and inthis way secures the cover component 20 against the stop 38 inside theaccumulator housing 10.

In order not to endanger the secure position of the cover component 20in the accumulator housing 10 and also to protect the cover component 20from introduction of harmful forces, the free longitudinal edge 32 is,as shown in FIG. 2, guided along its free end so as to project over thesecond side 40 of the cover component 20 positioned above. After therespective clamp connection has been secured, the shaping tool 42 ismoved back away from the accumulator housing 10 and then, for example,assumes its upper position as illustrated in FIG. 2. By preference theshaping process for the respective longitudinal edge 32 of theaccumulator housing 10 is effected as cold forming, but hot forminginvolving appropriate heating of the accumulator housing material andpreferably the shaping tool 42 as well is also conceivable. Aconventional easily shaped steel material is used as material for theaccumulator housing 10 with its longitudinal edge 32. In order tointroduce the clamping forces optimally into the cover component 20 andalso to ensure optimal support for the cover component 20 in theaccumulator housing 10 on the edge side provision is made such that theheight of the cover component 20 is adapted to the applicationconditions assigned by operation of the accumulator. In the caseillustrated the cover component 20 is at least twice as great as thelength of the longitudinal edge 32 between its free end and a deflectionpoint 54 from which the longitudinal edge 32 is moved to the top of thecover.

As is illustrated in FIG. 7 for a modified embodiment, the covercomponent 20 may nevertheless project beyond the longitudinal edge 32 ofthe accumulator housing 10, or, in another embodiment not shown, may endso as to be flush at the same level.

In one especially preferred embodiment (not shown) of the method claimedfor the invention, the fastening process for the respective end covercomponent 20, 22 is carried out in a common positioning movement of twoshaping tools 42 on opposite sides of the accumulator housing 10simultaneously and with more or less equal shaping forces by acting onthe respective free longitudinal edge 32 of the accumulator housing 10.It has been found that in the case of the respective shaping solutionthe opposite shaping tool can during shaping receive the forces of theother shaping tool such as occur during the forming process. Costlysupport devices may be dispensed with in this configuration on therespective opposite sides where the shaping tool 42 exerts no effect.Harmonious introduction of forces into the accumulator housing 10without the occurrence of damaging power peaks also occur in thissituation.

As is shown in FIGS. 3 and 4, the respective cover component 20, 22 maybe introduced into the accumulator housing 10 up to the stop 38 in theform of an annular surface, by means of a positioning tool 56, which, asis shown in FIG. 4, encloses the free longitudinal edge 32 of theaccumulator housing 10. The positioning tool 56 has for the respectiveintroduction process a feed bevel 58 along which the cover component 20,22 may slide on the external circumference side. Use of the positioningtool 56 permits reliable prevention of possible damage to the seal 34 ofthe respective cover component 20,22. In addition to the feed bevel 58the positioning tool 56 has an admission space 60 into which the upperend of the accumulator housing 10 may be introduced so that the feedbevel 58 ends flush with the upper edge of the longitudinal edge and inaddition effects uninterrupted transition to the admission area 62 forthe cover component 20, 22 itself in the accumulator housing 10.

In the embodiments shown in FIGS. 5 and 6 the accumulator housing 10 isprovided on the inner circumference side along its upper longitudinaledge 32 with an insertion bevel 50 which extends the length of theaccumulator housing 10 outward, this resulting in a sort of slip edgeover which the respective cover component 20, 22 may also be introducedand later secured. The respective alternative may be selected if thecover seal 34 is proved to be rugged and not overly susceptible todamage.

The same reference numbers are used for the same structural partsillustrated in FIG. 7; the method employed is described only to theextent that it differs significantly from the method as presented in theforegoing. In the instance of the embodiment shown the upper covercomponent 20 is retained by the free longitudinal edge 32 of theaccumulator housing 10 so that the upper side projects an assigneddistance beyond the end of the free longitudinal edge 32. In theembodiment shown in FIG. 7 the stop 38 for the cover component 20 isprovided with a bevel against which the cover component 20 leans in astepped recess. The annular seal 34 is in turn received in the outercircumference of the recessed sectional step 64; because of the steppedarrangement illustrated of accumulator housing 10 and cover component20, the possibility exists of machining the accumulator housing 10 asfinely as possible for clean contact with the sealing ring 34 at thispoint and of leaving the inside of the accumulator housing 10 more orless unmachined, insofar as the delivery area for the free longitudinaledges 32 of the accumulator housing 10 is affected.

The cover components 20, 22 may accordingly be fastened with highfitting accuracy, reliably, and pressure-tightly in the accumulatorhousings 10 by the shaping process discussed, in the widest possiblevariety of embodiments, while screw connections cost-intensive inmounting, which in addition remain to be secured in this position, maybe dispensed with in their entirety.

1. A method for the production of piston-type accumulators having anaccumulator housing (10) and a separating piston (12) displaceable inthe longitudinal direction in the accumulator housing (10) whichseparates two working chambers (16, 18) from each other inside theaccumulator housing (10), and which accumulator housing is sealed oneach of the end sides by a cover component (20, 22), characterized inthat on one side (40) of the cover component (20, 22) such covercomponent is fastened by way of the free longitudinal edge (32) of theaccumulator housing (10), which for this purpose undergoes a positioningmovement onto the cover component (20, 22).
 2. The method as claimed inclaim 1, wherein one side (36) opposite one side (40) of at least one ofthe two cover components (20, 22) is inserted into the accumulatorhousing (10) so as to come to rest against a stop (38) and/or whereinthe respective cover component (20, 22) is retained in its end positionby the clamping force of the positioned free longitudinal edge (32). 3.The method as claimed in claim 1, wherein a shaping tool (42) isprovided for the positioning movement of the longitudinal edge (32) ofthe accumulator housing (10), which shaping tool (42) which positionsthe longitudinal edge (32) provided with least one positioning bevel(44) on the cover component (20) in such a way that this cover component(20) is secured in the accumulator housing (10) as a kind of clampingseat.
 4. The method as claimed in claims 1, wherein the wall thicknessof the longitudinal edge (32) is reduced in relation to that of theremainder of the accumulator housing (10) and wherein the point oftransition between the different wall thicknesses forms the stop (38)for the cover component (20) inside the accumulator housing (10).
 5. Themethod as claimed in claims 1, wherein the longitudinal edge (32) isprovided with an insertion bevel (50) on its side facing the respectivecover component (20, 22) and toward the exterior.
 6. The method asclaimed in claims 1, wherein there is provided on the opposite side (40)of the cover component (20, 22) a contact surface (46), in particular inthe form of a securing bevel against which the longitudinal edge (32)rests in the secured state and wherein the cover component (20, 22)closes off the accumulator housing (10) from the exterior.
 7. The methodas claimed in claims 3, wherein two shaping tools (42) in a jointpositioning movement execute the securing process for the respectivecover component (20, 22) on opposite sides of the accumulator housing(10) by acting on the respective free longitudinal edge (32) of theaccumulator housing (10).
 8. The method as claimed in claims 1, whereinthe cover component (20, 22) is introduced into the accumulator housing(10) up to the stop (38) by means of a feed bevel (58), by means of apositioning tool (56) which encloses the free longitudinal edge (32) ofthe accumulator housing (10).
 9. The method as claimed in claims 1,wherein the longitudinal edge (32) is provided on the internalcircumference side with an insertion bevel (50) widening toward theexterior for the cover component (20, 22).
 10. The method as claimed inclaims 1, wherein the height selected for the cover component (20,22) isat least twice as great as the free longitudinal; edge (38) of theaccumulator housing (10) introduced for the purpose of clamping thecover component (20, 22).